Optically pumped, surface-emitting semiconductor laser device and method for the manufacture thereof

ABSTRACT

The invention is directed to an optically pumped surface-emitting semiconductor laser device having at least one radiation-generating quantum well structure and at least one pump radiation source for optically pumping the quantum well structure, whereby the pump radiation source comprises an edge-emitting semiconductor structure. The radiation-generating quantum well structure and the edge-emitting semiconductor structure are epitaxially grown on a common substrate. A very efficient and uniform optical pumping of the radiation-generating quantum well structure is advantageously possible with this monolithically produced semiconductor laser device. Methods for manufacturing inventive semiconductor laser devices are also specified.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to an optically pumped surface-emittingsemiconductor laser device having at least one radiation-generatingquantum well structure and at least one pump radiation source foroptically pumping the quantum well structure, whereby the pump radiationsource comprises an edge-emitting semiconductor structure.

2. Description of the Related Art

A semiconductor laser device of the species initially described isdisclosed by U.S. Pat. No. 5,991,318. An optically pumped verticalresonator semiconductor laser having a monolithic surface-emittingsemiconductor layer structure is disclosed therein. Given this knowndevice, the optical pump radiation, whose wavelength is shorter thanthat of the generated laser emission, is supplied by an edge-emittingsemiconductor laser diode. The edge-emitting semiconductor laser diodeis externally arranged such that the pump radiation is beamed obliquelyin from the front into the intensification region of thesurface-emitting semiconductor layer structure.

A particular problem given this known device is comprise therein thatthe pump laser must be exactly positioned relative to thesurface-emitting semiconductor layer structure and, additionally,requires an optical means for beam focusing in order to image the pumpradiation exactly into the desired region of the surface-emittingsemiconductor layer structure. These measures involve considerabletechnological outlay.

In addition to the losses at the optics, moreover, coupling losses alsooccur that reduce the overall efficiency of the system.

Another problem is comprised therein that only a few quantum wells canbe excited by pump radiation due to the pumping from the front.

SUMMARY OF THE INVENTION

The object of the present invention is comprised in making available asemiconductor laser device of the species initially cited withsimplified adjustment of the pump source and surface-emitting layerstructure and with high output power. Further, a technically simplemethod for manufacturing such a device is recited.

According to the invention, the radiation-generating quantum wellstructure and the edge-emitting semiconductor structure are epitaxiallygrown on a common substrate given an optically pumped surface-emittingsemiconductor laser device of the species initially cited. The layerthicknesses of the individual semiconductor layers can be very exactlyset in the epitaxy, so that a high positioning precision of theedge-emitting semiconductor structure relative to theradiation-generating quantum well structure is advantageously achieved.

With the inventive device, further, a uniform optical pumping of thequantum well structure can be achieved for high output powers in thefundamental mode.

In an advantageous embodiment, the surface-emitting quantum wellstructure and the pump radiation source are arranged side-by-side on thesubstrate such that a radiation-emitting region of the pump radiationsource and the quantum well structure lie at the same height above thesubstrate. What is thereby achieved is that pump radiation is laterallycoupled into the quantum well structure during operation of thesemiconductor laser device. This means that the beam axis of the pumpradiation proceeds essentially parallel to the substrate surface and,thus, essentially vertically relative to the beam axis of the laser beamgenerated by the surface-emitting semiconductor laser device.

Given such a device, the quantum well structure is “pumped”transparently at first from the lateral surfaces during operation until,finally, the entire lateral cross-sectional area thereof is laseractive. Due to the lateral optical pumping, moreover, a uniform fillingof the quantum wells with charge carriers is achieved.

Preferably, the quantum well structure is surrounded by theedge-emitting semiconductor structure. At least one gain-guidedradiation-emitting active region that serves as a pump radiation sourceis formed therein on the basis of at least one current injection path onthe surface of the semiconductor laser structure. Alternatively, atleast one index-guided radiation-emitting active region of theedge-emitting semiconductor structure serves as the pump radiationsource. This is defined, for example, with at least one currentinjection path on the surface of the edge-emitting semiconductorstructure in combination with, for example, etched trenches in thesemiconductor structure fashioned along the current injection path.

Preferably, the ends of the current injection path facing toward theradiation-generating quantum well structure have a spacing of 10 μthrough 50 μm, especially preferred approximately 30 μm. As a resultthereof, disturbing leakage currents and other disturbing influences atthe boundary surfaces between the edge-emitting semiconductor structureand the surface-emitting layer sequence, i.e. the input surfaces for thepump radiation, are reduced.

The aforementioned embodiments can be advantageously fabricated overallwith traditional semiconductor process technology.

When, during operation of the device, an adequately high current flowsthrough the injection paths into the active layer of the pump radiationsource, an intensified spontaneous emission (super-radiation) is formed,this being guided into the surface-emitting laser region and beingabsorbed thereat. The electron-hole pairs generated as a result thereofare collected in the quantum well and lead to the inversion in theintensification region of the surface-emitting laser structure.

The excitation of the surface-emitting laser structure can ensue bypumping the quantum well structure or confinement layers adjacentthereto. When pumping the confinement layers, the pump efficiency ispreferably enhanced in that the band gap thereof decreases toward thequantum well structure. This, for example can be achieved by modifyingthe material composition. As a result thereof, internally electricalfields are generated in the confinement layers that drive the opticallygenerated charge carriers into the active quantum well region.

In an especially preferred embodiment, a plurality of pump radiationsources are arranged star-like around the quantum well structure, sothat the quantum well structure is transparently “pumped” andlaser-active over its entire lateral cross-section in a short time andvery uniformly.

The boundary surface between edge-emitting semiconductor structure andquantum well structure is preferably at least partially reflective. Whatis thereby achieved is that a back-reflection into the edge-emittingsemiconductor structure derives at the edge to the surface-emittinglaser region, this leading to the formation of laser radiation in thepump source and, thus, to enhanced pump efficiency.

Generating laser radiation as pump radiation and, thus, enhanced pumpefficiency is alternatively achieved in that respectively two pumpradiation sources arranged at opposite sides of the quantum wellstructure together form a laser structure. The end faces of theedge-emitting radiation sources lying parallel to one another and facingaway from the quantum well structure are fashioned as mirror surfacesfor this purpose and serve as a resonator mirror. These, for example,can be generated by cleaving and/or etching (for example, dry etching)and can be provided with a passivation layer and/or can be highlyreflectively mirrored.

The opposite pump radiation sources are coupled during operation via thetransparently pumped quantum well structure to form a single, coherentlyresonating laser. Given optimum end mirroring, the entire optical powerstored in the pump laser is then available as pump power except for thelosses at the boundary surfaces between the pump laser andsurface-emitting laser.

Preferably, the edge-emitting semiconductor structure comprises a largeoptical cavity (LOC) structure. Given this, an active layer is embeddedbetween a first and a second waveguide layer that are in turn embeddedbetween a first and a second cladding layer.

In an advantageous development of the invention, it is provided that theedge-emitting semiconductor structure be fashioned as a ring laser.Here, a ring laser is a laser structure wherein ring modes can formduring operation. The design of the appertaining laser resonator in ringform is thereby advantageous, as to be explained below, but notcompulsory.

The resonator of such a ring laser can be formed with totally reflectiveboundary surfaces, so that no highly reflective mirrors are required.The risk of a lower radiation yield due to damage at the mirrors is thusalso reduced. Further, a ring laser is distinguished by anadvantageously large mode volume and by a high mode stability.

Preferably, the quantum well structure to be pumped is arranged withinthe ring resonator, so that the entire resonator-internal radiationfield is available for pumping the quantum well structure. It is therebyespecially advantageous to arrange the active layer of the edge-emittingsemiconductor structure and the quantum well structure at the sameheight above the substrate, so that a large overlap derives between thevolume of the quantum well structure to be pumped and the radiationfield of the edge-emitting semiconductor structure and, thus, a highpump efficiency derives.

In an advantageous development of the invention, the resonator of thering laser is formed by an annularly closed waveguide. The guidance ofthe pump radiation field therein ensues by total reflection at thelimitations of the waveguide, so that highly reflective mirrors are alsoadvantageously not required here. Further, the pump radiation field canbe very well-adapted to the volume of the quantum well structure to bepumped as a result of the shaping of the annularly closed waveguide.

The edge-emitting semiconductor structure in a preferred development ofthe invention is surrounded by a medium whose refractive index is lowerthan the refractive index of the semiconductor structure. As a resultthereof, a totally reflective surface that serves as a limitation of thelaser resonator arises at the transition from the semiconductor into theoptically thinner, surrounding medium. For forming an annularly closedwaveguide, a recess filled with the optically thinner medium can bearranged within the edge-emitting semiconductor structure.

Due to the low refractive index, air or some other gaseous medium isparticularly suitable as the surrounding medium. Alternatively, theedge-emitting semiconductor structure can also be surrounded by someother materials such as, for example, a semiconductor material, asemiconductor oxide or a dielectric having a lower refractive index.

Preferably, the semiconductor structure is formed as a cylindrical stackof circular or annular semiconductor layers. The cylindricalsemiconductor body shaped in this way simultaneously represents the ringlaser resonator at whose cladding surfaces the radiant field is guidedin totally reflecting fashion.

Alternatively, the semiconductor structure can also be formedprismatically as a stack of semiconductor layers in the form of polygonsor polygonal rings. As a result of this shaping, a largely uniform beamdistribution and, correspondingly, a largely homogeneous pump densitycan be achieved in the quantum well structure.

A stack of semiconductor layers of the described shape can be formedcomparatively simply, for example by etching from a previouslyepitaxially produced semiconductor layer sequence. Advantageously, thelaser resonator of the edge-emitting semiconductor structure issimultaneously also formed with the shaping of the semiconductor bodywithout additional mirrorings being required.

In an especially preferred development of the semiconductor device, thequantum well structure has more than ten quantum wells. This high numberof quantum wells is possible because all quantum wells are directlypumped as a result of the lateral input of the pump radiation. As aresult thereof, a high gain in the surface-emitting quantum wellstructure is advantageously achieved.

The edge-emitting semiconductor structure is preferably fashioned suchthat it generates a pump wave whose maximum lies at the height of thequantum wells above the substrate, especially preferably at the level ofthe center of the quantum well structure.

In order to obtain especially high output powers, the edge-emittingsemiconductor structure in an advantageous development is fashioned aswhat is referred to as a multiple stack or micro-stacked laser having aplurality of laser-active layer sequences (for example, doubleheterostructures) that are connected in series via tunnel transitions.The quantum well structure then advantageously comprises a plurality ofquantum well groups that respectively lie at the height of alaser-active layer sequence of the pump source.

In a preferred method for manufacturing an optically pumped,surface-emitting semiconductor laser device according to theaforementioned embodiments, a first semiconductor layer sequencesuitable for a surface-emitting semiconductor laser and having at leastone quantum well structure is initially applied onto a substrate.Subsequently, the first semiconductor layer sequence is removed outsidethe intended laser region. An edge-emitting, second semiconductor layersequence is deposited subsequently on the region over the substrate thatwas uncovered after the removal of the first semiconductor layersequence, the second semiconductor layer sequence being suitable forgenerating pump radiation and transmitting it into the quantum wellstructure. Subsequently, at least one current injection path isfashioned in the edge-emitting semiconductor layer sequence.

Preferably, a buffer layer is first applied onto the substrate. A firstconfinement layer is deposited thereon. A quantum well structuresuitable for a surface-emitting semiconductor laser is subsequentlyapplied onto the first confinement layer and this quantum well structureis followed by a second confinement layer. After the removal of theconfinement layers and of the quantum well structure and, partially, ofthe buffer layer outside the intended surface-emitting laser region, afirst cladding layer, a first waveguide layer, an active layer, a secondwaveguide layer and a second cladding layer are successively appliedonto the region of the buffer layer that is then uncovered. Therespective layer thicknesses are designed such that the pump radiationgenerated in the active layer proceeds into the quantum well structure.

In another embodiment of the semiconductor laser device according to theinvention, the radiation-emitting quantum well structure and the pumpradiation source are arranged above one another on the substrate. Thequantum well structure is thereby optically coupled to the edge-emittingsemiconductor structure, so that pump radiation from the pump radiationsource is guided into the quantum well structure during operation of thesemiconductor laser device.

The edge-emitting semiconductor structure preferably comprises a firstwaveguide layer and—as viewed from the substrate—a second waveguidelayer following thereupon between which an active layer is arranged. Thequantum well structure is epitaxially grown on the second waveguidelayer, covers only a sub region of the edge-emitting semiconductorstructure and is optically coupled thereto.

For improving the infeed of the pump radiation into the quantum wellstructure, the boundary surface between second waveguide layer andadjacent cladding layer is bent or buckled toward the quantum wellstructure in the proximity of the surface-emitting laser region.

In order to improve the infeed of the pump radiation into thesurface-emitting semiconductor structure, the refractive index of thesecond waveguide layer is advantageously higher than the refractiveindex of the first waveguide layer and/or the active layer is placedsymmetrical in the waveguide fashioned by the two waveguide layers.

Analogous to the above-described, first embodiment, one or moregain-guided and/or index-guide, radiation-emitting active regions arefashioned as pump radiation sources in the edge-emitting semiconductorstructure.

In a preferred method for manufacturing an optically pumped,surface-emitting semiconductor laser device according to theaforementioned, second basic embodiment and the developments thereof, anedge-emitting semiconductor laser layer sequence is first applied onto asubstrate. A surface-emitting semiconductor laser layer sequence havingat least one quantum well structure is then applied thereon.Subsequently, the surface-emitting semiconductor laser layer sequence isremoved outside the intended laser region before at least one currentinjection path is fashioned in the edge-emitting semiconductor layersequence.

To this end, a buffer layer is preferably first applied onto thesubstrate.

Subsequently, a first waveguide layer, an active layer and a secondwaveguide layer are deposited successively thereon. A first confinementlayer, a surface-emitting semiconductor laser layer sequence having aquantum well structure and a second confinement layer are applied ontothe edge-emitting layer sequence produced in this way. The confinementlayers, the surface-emitting semiconductor laser layer sequence and, inpart, the second waveguide layer are then removed outside the intendedsurface-emitting laser region.

In an inventive method for manufacturing an optically pumped,surface-emitting semiconductor laser device having a ring laser as apump radiation source, a surface-emitting semiconductor layer sequencehaving at least one quantum well structure—as already set forth isinitially applied on a substrate, the layer sequence is removed outsidethe planned laser region, and the edge-emitting semiconductor structureof the pump radiation source is applied onto the region uncovered as aresult thereof.

Subsequently, the outside region of the edge-emitting semiconductorstructure is removed for shaping the laser resonator. A centralsub-region in the inside of the semiconductor structure is thereby alsopreferably eroded for forming a ring resonator. The removal of thesub-regions can, for example, ensue with a dry etching process.Advantageously, a complicated post-processing of the etched surfaces isnot required.

Alternatively, the method steps can also be applied in a differentsequence. For example, an edge-emitting semiconductor structure can beapplied first on the substrate, this then being eroded in the plannedlaser region of the quantum well structure (which is yet to be formed).In the next step, the surface-emitting semiconductor layer sequencehaving at least one quantum well structure is applied on the uncoveredregion. Subsequently, the outside region of the edge-emittingsemiconductor structure is again removed for shaping the laserresonator. In a modification of the method, the shaping of the laserresonator can also occur before the application of the surface-emittingsemiconductor layer sequence.

In a preferred development of the two above-recited embodiments, ahighly reflective Bragg reflector layer sequence is fashioned at oneside of the quantum well structure, this representing a resonator mirrorof the surface-emitting laser structure. A further Bragg reflector layersequence or an external mirror is arranged at the opposite side of thequantum well structure as second, partially transmissive resonatormirror.

Preferably, the substrate is composed of a material that is transmissivefor the laser beam generated in the semiconductor laser device, and thehighly reflective Bragg reflector is arranged at that side of thequantum well structure facing away from the substrate. This enables ashort connection between the semiconductor structures and a heat sinkand, thus, a good heat elimination from the semiconductor structures.

In order to prevent disturbing transverse modes (modes parallel to thesubstrate—whispering modes), absorber layers are arranged in the edgeregion and/or in etching structures of the surface-emittingsemiconductor laser layer sequence.

The inventive semiconductor laser device is particularly suitable foremployment in an external resonator wherein a frequency-selected elementand/or a frequency doubler is located.

Advantageously, the inventive semiconductor laser device—via modulationof the pump laser—can be modulated by modulation of the pump current orvia a short-circuit connection of the surface-emitting semiconductorlaser layer sequence.

Further advantageous developments and improvements of the device and ofthe method of the invention derive from the exemplary embodimentsdescribed below in conjunction with FIGS. 1 through 14.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic illustration of a section through a firstexemplary embodiment.

FIGS. 2 a through 2 e show a schematic illustration of a method sequencefor manufacturing the exemplary embodiment according to FIG. 1.

FIG. 3 a shows a schematic illustration of a section through a secondexemplary embodiment.

FIG. 3 b shows a schematic illustration of an advantageous developmentof the waveguide of the exemplary embodiment according to FIG. 3 a.

FIGS. 4 a through 4 c show a schematic illustration of a method sequencefor manufacturing the exemplary embodiment according to FIG. 3.

FIG. 5 shows a schematic illustration of a plan view onto a firstarrangement of current injection paths on an edge-emitting semiconductorstructure.

FIG. 6 shows a schematic illustration of a plan view onto a secondarrangement of current injection paths on an edge-emitting semiconductorstructure.

FIG. 7 shows a schematic illustration of a plan view onto a thirdarrangement of current injection paths on an edge-emitting semiconductorstructure.

FIGS. 8 a and 8 b show a schematic illustrations of semiconductor laserdevices with absorber layer.

FIGS. 9 a and 9 b show a schematic illustration of a section and of aplan view of a first exemplary embodiment having a ring laser as pumpradiation source.

FIG. 10 shows a schematic illustration of a plan view of a secondexemplary embodiment having a ring laser as pump radiation source.

FIGS. 11 a and 11 b show a schematic illustration of a plan view of athird and fourth exemplary embodiment having respectively two ringlasers as pump radiation sources.

FIGS. 12 and 12 b show a schematic illustration of a method sequence formanufacturing the exemplary embodiment according to FIG. 9.

FIG. 13 shows a schematic illustration of an inventive semiconductorlaser device having an external resonator.

FIG. 14 shows a schematic illustration of a modulatable semiconductorlaser device of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Identical elements or elements having the same effect are provided withthe same reference characters in the Figures.

The exemplary embodiment of FIG. 1 is, for example, an optically pumpedsurface-emitting semiconductor laser chip having a laser emission at1030 nm. Therein, a buffer layer 6 is applied on a substrate 1. Thesubstrate 1 is composed, for example, of GaAs and the buffer layer 6 iscomposed of undoped GaAs.

A surface-emitting semiconductor laser structure 10 having a quantumwell structure 11 is applied on the buffer layer 6 centrally over thesubstrate, this representing the surface-emitting laser region 15. Thesemiconductor laser structure 10 is composed of a first confinementlayer 12 located directly on the buffer layer 6, of a quantum wellstructure 11 arranged on the confinement layer 12 and of a secondconfinement layer 13 applied on the quantum well structure 11.

The confinement layers 12 and 13 are composed, for example, of undopedGaAs, and the quantum well structure 11 comprises, for example, aplurality (≧3) of quantum wells that are composed of undoped InGaAswhose thickness is set to the emission at 1030 nm and between whichbarrier layers of GaAs are located.

A Bragg mirror 3 having, for example, 28 through 30 periods GaAIAs(10%AI)/GaAlAs (90% Al) that represents a highly reflective resonatormirror is deposited over the surface-emitting semiconductor laserstructure.

An edge-emitting semiconductor laser structure 21, for example a largeoptical cavity (LOC) single quantum well (SOW) laser structure for anemission at approximately 1 μm, is deposited in the environment of thelaser region 15 on the buffer layer 6. This structure 21 is composed,for example, of a first cladding layer 28 (for example,n-GaAl_(0.65)As), of a first waveguide layer 23 (for example,n-GaAl_(0.1)As), of an active layer 25 (for example, an undopedInGaAs-SQW), of a second waveguide layer 24 (for example,p-GaAl_(0.1)As) and of a second cladding layer 29 (for example,p-GaAl_(0.65)As).

For example, a p⁺-doped GaAs layer can be applied on the second claddinglayer 29 as a cover layer 30.

The LOC region 22 is arranged at the same height as the quantum wellregion of the surface-emitting laser structure 10; preferably, theactive layer 25 is located at the same height above the substrate 1 asthe quantum well structure 11.

In a particular embodiment of the exemplary embodiment, theedge-emitting semiconductor structure 21 comprises a plurality of activelayers 25 that are connected in series via tunnel transitions. Analogousthereto, the quantum well structure 11 comprises a plurality of quantumwell groups that respectively lie at the height of an active layer 25 ofthe edge-emitting semiconductor structure 21.

All semiconductor layers are, for example, produced with metallorganicvapor phase epitaxy (MOVPE).

In the mirrors 31 proceeding perpendicular to the layers of theedge-emitting semiconductor laser structure 21 are located in theproximity of the outer edge of the edge-emitting semiconductor laserstructure 21, these end mirrors 31 extending at least into the firstcladding layer 28, here up to the buffer layer 6, proceeding from thecover layer 30. For example, these are produced after the growth of theedge-emitting semiconductor laser structure 21 by etching (for example,reactive ion etching) of corresponding trenches and the subsequentfilling thereof with highly reflective material. Respectively twomirrors 31 parallel to one another are arranged at opposite sides of thequantum well structure 11 (see FIGS. 5 and 6).

Alternatively, the end mirrors can be manufactured in a known way bycleaving along crystal planes. As shown in FIG. 1, these are then notnecessarily arranged in the chip but are formed by the cleaved chiplateral surfaces (see FIG. 7).

In electrically insulating mask layer 7, for example a silicon nitride,an aluminum oxide or a silicon oxide layer, with which current injectionpaths 26 of the edge-emitting semiconductor laser structure 21 aredefined are located on the free surface of the cover layer 30 and of theBragg mirror 3 (see FIGS. 5 and 6. A p-contact layer 32, for example aknown contact metallization, is applied on the mask layer 7 and—in therecesses thereof for the current injection paths 26—on the cover layer30.

For example, six stripe arrays each having 15 stripes (4 μm stripe, 10 μpitch) with approximately 150 μm active width that are arrangedsymmetrically star-shaped around the surface-emitting laser region 15are selected for the pump source.

Preferably, the ends of the current injection paths 26 facing toward theradiation-generating quantum well structure 11 have a spacing of 10 μmthrough 50 μm, particularly preferably of approximately 30 μm,therefrom. As a result thereof, disturbing leakage currents and otherdisturbing influences at the boundary surfaces between the edge-emittingsemiconductor structure 21 and the surface-emitting layer sequence 10are reduced, i.e. at the infeed surfaces for the pump radiation 2.

All current injection paths 26 can be provided with a common p-contactlayer 32, as a result whereof the radiation-emitting regions of theedge-emitting structure are connected parallel to one another inoperation. Given an intended, separate drive of these individualradiation-emitting regions, a correspondingly structured p-conductive,first contact layer 32 is applied. As a result thereof, an optimizedpump light distribution (for example, similar to a Gauss profile) can beproduced over the lateral cross-section of the surface-emittingstructure.

For generating index-guided pump regions in the edge-emitting structure21, trenches manufactured, for example, by etching can be formed thereinalong the current injection paths 26 (the trenches being shown in theFIGS. 5 and 6), these extending, for example, up to 0.5 μm into thesecond waveguide layer 24. As a result thereof, an improved waveguidance is achieved at the edges of the pump regions.

The principal surface 16 of the substrate 1 facing away from thesemiconductor structure is provided with an n-conductive, second contactlayer 9, for example likewise a known contact metallization, except foran exit window 8 for the laser beam (indicated with the arrow 5).

The principal surface 16 of the substrate is preferably anti-bloomed inthe region of the exit window 8 in order to reduce back-reflections intothe chip.

A laser resonator of the surface-emitting laser structure 10 can befashioned as a Bragg mirror 3 and an external, further mirror (not shownin FIG. 1) arranged at the opposite side of the substrate 1 or can beformed of a further Bragg mirror arranged between the substrate 1 andthe quantum well structure 11.

During operation of the semiconductor chip, pump radiation (indicated bythe arrows 2) is generated in a region of the edge-emittingsemiconductor structure 21 that represents the pump radiation source 20and that are defined by the current injection paths 26, and this pumpradiation is coupled into the quantum well structure 11 of thesurface-emitting laser structure 10.

Given adequate back-reflection at the boundary surface between theedge-emitting structure 21 and the surface-emitting structure 10 and asuitable position of the end mirrors 31, laser radiation that leads toan enhanced pump efficiency is generated in the edge-emitting structure21.

Preferably, the end mirrors 31 are arranged such relative to one anotherthat these form a laser resonator for two radiation-emitting regions ofthe edge-emitting structure 21 that lie opposite one another. The tworadiation-emitting regions lying opposite one another are then coupledto form a single coherently resonating laser after the transparentpumping of the surface-emitting laser structure 10. Given optimummirroring of the end mirrors 31, the entire optical power generated bythe pump laser is available as pump power except for losses at theboundary surface between the edge-emitting structure 21 and thesurface-emitting structure 10.

Given the method schematically shown in FIGS. 2 a through 2 e formanufacturing the exemplary embodiment according to FIG. 1, the bufferlayer 6, the first confinement layer 12, the quantum well structure 11,the second confinement layer 13 and the Bragg mirror layers 3 areinitially successively applied onto the substrate 1, for example byMOVPE (FIG. 2 a).

Subsequently, an etching mask 17 (for example, a Si-nitride mask), isapplied onto the region of this layer sequence provided as asurface-emitting laser region 15. Subsequently, the Bragg mirror layers3, the confinement layers 12 and 13, the quantum well structure 11 and,in part, the buffer layer 6 are removed, for example by etching, forexample dry-etching with Cl chemistry, outside the intendedsurface-emitting laser region 15 (FIG. 2 b). The first cladding layer28, the first waveguide layer 23, the active layer 25, the secondwaveguide layer 24, the second cladding layer 29 and the cover layer 30are successively applied then on the uncovered region of the bufferlayer 6, for example again with MOVPE (FIG. 2 c).

With, for example, reactive ion etching and suitably known masktechnology, trenches for the end mirrors 31 are then etched (see FIG. 2d) in the most recently applied edge-emitting structure 21, thesetrenches being subsequently coated or filled with reflection-enhancingmaterial. The etching mask 17 is also removed.

Subsequently, the electrically insulating mask layer 7 is applied ontothe cover layer 30 and onto the Bragg mirror 3 before the p-contactlayer 32 and the n-contact layer 9 are finally produced (FIG. 2 e).

Before the application of the insulating mask layer 7, the trenchesdescribed above in conjunction with FIG. 1 are optionally produced forgenerating index-guided pump lasers, being produced by etching.

In order to reduce radiation losses, the substrate 1 is preferablythinned to less than 100 μm or completely removed after the MOVPE.

In the exemplary embodiment according to FIG. 3, a buffer layer 6 isinitially situated surface-wide on the substrate 1 and an edge-emittingsemiconductor laser structure 21 is arranged thereon surface-widewherein an active layer 25 is arranged between a first waveguide layer23 and a second waveguide layer 24.

In a planned laser region 15 over the middle of the substrate 1, asurface-emitting quantum well structure 11 is grown on the secondwaveguide layer 24 followed by a confinement layer 13 and a Bragg mirrorlayer sequence 3.

An electrically insulating mask layer 7 that comprises recesses forcurrent injection paths 26 of the edge-emitting structure 21 (see FIG.7) is applied in the region around the laser region 15 onto the secondwaveguide layer 24 or, potentially, onto a highly doped cover layerapplied thereon. A first contact layer 32 is located on the electricallyinsulating mask layer 7 and in the recesses thereof on the secondsemiconductor layer or, on the cover layer and a second contact layer 9having an exit window for the laser beam (indicated with the arrow 5) isarranged at that side of the substrate 1 lying there opposite.

For producing index-guided pump regions in the edge-emitting structure21, trenches manufactured, for example, by etching can be fashioned(shown in the FIGS. 5 and 6) in the second waveguide layer 24 along thecurrent injection paths 26. An improved waveguidance at the edges of thepump regions is achieved as a result thereof.

Cleaved sidewalls of the chip, for example, are provided here as endmirrors 31 of the edge-emitting structure 21.

During operation, pump laser radiation is generated in the edge-emittinglaser structure, a part thereof being coupled into the quantum wellstructure 11 lying thereabove.

In order to promote the infeed, the active layer 25 is asymmetricallylocated in the waveguide formed by the two waveguide layers 23 and 24.Alternatively or additionally, the refractive index of the secondwaveguide layer 24 can be higher than that of the first waveguide layer23 and/or the second waveguide layer can be pulled up toward the laserregion 15 in the direction of the quantum well structure 11 for the samepurpose (See FIG. 3 b).

The materials recited for the corresponding layers of the exemplaryembodiment according to FIG. 1 can be used by way of example here asmaterials for the various layers.

A laser resonator of the surface-emitting laser structure 10 can also beformed in this exemplary embodiment from the Bragg mirror 3 and from anexternal, further mirror (not shown in FIG. 3 a) arranged at theopposite side of the substrate 1 or a further Bragg mirror arrangedbetween the substrate 1 and the quantum well structure 11.

Given the method for manufacturing a device according to the exemplaryembodiment of FIG. 3 a that is schematically shown in FIGS. 4 a through4 c, a buffer layer 6 is first applied onto the substrate 1. The firstwaveguide layer 23, the active layer 25 and the second waveguide layer24 are subsequently successively grown thereon. Subsequently, thequantum well structure 11 is grown onto the second waveguide layer 24,followed by the confinement layer 13 and the Bragg mirror layer 3 (FIG.4 a). These layers are produced, for example, with MOVPE.

Subsequently, an etching mask 17 is applied onto the sub-region of thelayer sequence that has been grown and that is provided as laser region15, and the Bragg mirror layer 3, the confinement layer 13, the quantumwell structure 11 and, in part, the second waveguide layer 24 areremoved outside the laser region 15 with etching (FIG. 4 b).

Subsequently and for definition of the current injection paths 26, theelectrically insulating mask layer 7 is applied onto the secondwaveguide layer 24 before the contact layer 32 is then deposited.

Subsequently, the second contact layer 9 having an exit window 8 isapplied onto the principal surface of the substrate 1 lying opposite thesemiconductor layer sequence (FIG. 4 c).

In order to reduce radiation losses, the substrate 1 here is alsopreferably thinned too, for example, less then 100 μm or is completelyremoved following the MOVPE.

The inventive, so-called wafer lasers are preferably soldered with theBragg mirror down onto a heat sink. One electrode is located on the heatsink and the second is generated by bonding on the wafer laser surface.

In order to prevent disturbing transverse modes (modes parallel to thesubstrate—whispering modes), absorber layers 18 (see FIGS. 8 a and 8 b)are arranged in the edge region and/or in etched structures of thesurface-emitting semiconductor laser layer sequence 15. Suitableabsorber materials for such applications are known and are therefore notexplained in greater detail here.

FIG. 9 a shows a section through an exemplary embodiment of an opticallypumped, surface-emitting semiconductor device having a ring laser as thepump radiation source. The sequence of the individual semiconductorlayers essentially corresponds to the exemplary embodiment shown in FIG.1.

Differing from the semiconductor device shown in FIG. 1, theedge-emitting semiconductor structure 21, comprising the first claddinglayer 28 (for example, n-GaAl_(0.65)As), the first waveguide layer 23(for example, n-GaAl_(0.1)As), the active layer 25 (for example,InGaAs-SQW), the second waveguide layer 24 (for example, p-GaAl_(0.1)As)and the second cladding layer 29 (for example, p-GaAl_(0.65)As), as aring laser.

The plan view onto the semiconductor body shown in FIG. 9 b illustratesthis.

The sectional view according to FIG. 9 a corresponds to a verticalsection along line A—A.

In the plan view, the edge-emitting semiconductor structure 21 comprisesan octagonal shape having four full rotational symmetry as well as aquadratic, central recess 38. The quantum well structure to be pumpedand which is circular in the plan view is completely arranged within theoctagonal ring formed in this way. This octagonal ring forms a ringresonator in the form of a totally reflective, closed waveguide.

During operation, cyclically circulating ring modes resonate in thiswaveguide, illustrated, for example, with reference to the modes 37 a, band c, these optically pumping the quantum well structure 11. As aresult of the total reflection at the outside surfaces, the outputlosses in this exemplary embodiment are extremely low, so that theentire resonator-internal radiation field is advantageously availablefor pumping the quantum well structure 11.

As a result of the illustrated shaping of the octagonal ring, the ringmodes 37 a, 37 b and 37 c are essentially of the same priority andpropagate uniformly. A largely uniform radiation field thus derives inthe radial direction (along the line B—B) and, correspondingly, alargely uniform pump density derives in the quantum well structure 11 tobe pumped.

The second mirror required for a laser mode of the surface-emittingsemiconductor laser structure 10 is not integrated in the semiconductorbody in the illustrated exemplary embodiment but is provided as anexternal mirror (also see FIG. 13). Alternatively, this second mirrorcan also be fashioned in the semiconductor body in a way (not shown)similar to the mirror 3. In this case, the second mirror would have tobe arranged, for example, within the provided laser region 15 betweenthe buffer layer 6 and the quantum well structure 11.

FIG. 10 shows another exemplary embodiment of an inventive semiconductorlaser device in plan view. Differing from the exemplary embodimentdescribed above, the totally reflective waveguide is fashioned as acircular ring here. The quantum well structure 11 to be pumped iscompletely arranged within the ring region.

A plurality of ring modes can resonate within the annular resonator. Theillustrated mode 39 merely indicates one possible example. The quantumwell structure 11, additionally, is pumped by a plurality of furthermodes with high efficiency.

As derives from FIG. 10, the central recess 38 can also be foregone forsimplification, so that the resonator comprises a solid circular area incross-section. As a result thereof, the manufacturing outlay isadvantageously reduced. However, modes that proceed through theresonator center can then resonate up to a certain extent. These modesare not totally reflected at the resonator limitation and therefore havecomparatively high output losses that ultimately reduce the pumpefficiency.

FIG. 11 a shows a further exemplary embodiment of the invention whereinthe quantum well structure 11 is pumped by two ring lasers that areindependent of one another. These are fundamentally constructed like thering laser of the first exemplary embodiment.

The appertaining waveguides 44 and 45 cross in two regions 46 a and b,whereby the quantum well structure 11 to be pumped is arranged in theregion 46 a.

The pump density in the quantum well structure 11 is enhanced furtherwith this arrangement having two ring lasers. The essential pump modesare again shown by way of example with reference to the modes 37 a, b,c, d, e and f. Advantageously, a largely uniform pump density againderives here as in the case of the first exemplary embodiment.

FIG. 11 b shows an advantageous version of the arrangement shown in FIG.3 a that is particularly distinguished in that the shaping of thecrossing, annular waveguides 44 and 45 is simplified. To that end, thecross-sections of the central recesses 40 and 41 are reduced totriangles. The lateral recesses 43 shown in FIG. 11 a and the centralrecess 42 are foregone. The manufacturing outlay is advantageouslyreduced as a result of this simplification without significantlydeteriorating the laser function.

As indicated in FIG. 11 b, a second quantum well structure 47 could,further, also be fashioned in the second crossing region 46 b of the tworing lasers.

FIG. 12 schematically shows two method steps for manufacturing aninventive semiconductor laser device.

As already described and shown in FIGS. 2 a, 2 b and 2 c, the methodbegins with the application of the buffer layer 6, of the firstconfinement layer 12, of the quantum well structure 11, of the secondconfinement layer 13 and of the Bragg mirror layers 3 on a substrate 1,for example with MOVPE. Subsequently, an etching mask 7 is applied ontothe region of this layer sequence provided as the surface-emitting laserregion 15, and the stack of Bragg mirror layers 3, confinement layers 12and 13, quantum well structure 11 and parts of the buffer layer 6outside the intended surface-laser region 15 are removed. The firstcladding layer 28, the first waveguide layer 23, the active layer 25,the second waveguide layer 24, the second cladding layer 29 and thecover layer 30 are successively applied onto the uncovered region of thebuffer layer 6, for example again with MOVPE (not shown, see FIGS. 2 a,b, c).

According to FIG. 12 a, subsequently, the outside regions and thecentral region of the semiconductor structure are eroded for forming thetotally reflective, closed waveguide. This, for example, can ensue withreactive ion etching upon employment of a suitable, known masktechnique.

The lateral surfaces of the edge-emitting semiconductor structuremanufactured in this way require no optical coating and forming a nearlyloss-free ring laser resonator.

Finally, the etching mask 17 is removed, the electrically insulatingmask layer 7 is applied onto the Bragg mirror 11 and the surface iscovered with a p-contact layer 32. The substrate is provided withn-contact surfaces 9 (FIG. 12 b).

The inventive semiconductor laser devices particularly suited foremployment in an external resonator with an external mirror 33 and apartially transmissive concave reflection mirror 34 in which afrequency-selected element 35 and/or a frequency doubler 36 is located(see FIG. 13).

Advantageously, the inventive semiconductor laser device can then bemodulated via modulation of the pump source (by modulating the pumpcurrent) or via a short-circuit connection of the surface-emittingsemiconductor laser layer sequence (FIG. 14).

The above-described structures can be employed not only in the InGaAlAsemployed by way of example but, for example, can also be employed in theInGaN, InGaAsP or in the InGaAlP system.

Given a wafer in the InGaN system for an emission at 470 nm, the quantumwells composed, for example InGaN for 450 nm emission, the confinementlayer are composed of InGaN with a reduced refractive index, and theBragg mirrors are composed of an InGaAlN system. The pump laserstructure comprises an active region with quantum wells of InGaN foremission at approximately 400 nm as well as waveguide layers andcladding layers of GaAlN, wherein the desired refractive indices are setby variation of the Al content.

Although other modifications and changes may be suggested by thoseskilled in the art, it is the intention of the inventors to embodywithin the patent warranted hereon all change and modifications asreasonably and properly come within the scope of their contribution tothe art.

1. An optically pumped surface-emitting semiconductor laser device,comprising: an external laser resonator; a radiation-generating quantumwell structure formed by a semi-conductor layer sequence, saidradiation-generating quantum well structure being provided forgenerating radiation in said external laser resonator, saidsemi-conductor layer sequence being epitaxially and successively grownon a common substrate, and a pump radiation source with a radiationregion for optically pumping the radiation generating quantum wellstructure, said pump radiation source including an edge-emittingsemiconductor structure comprising a first waveguide layer and a secondwaveguide layer and an active layer between said first and secondwaveguide layers, said edge-emitting semiconductor structure beingformed by the semi-conductor layer sequence being epitaxially andsuccessively grown on the common substrate.
 2. An optically pumpedsurface emitting semiconductor laser device according to claim 1,wherein the radiation generating quantum well structure and the pumpradiation source are being arranged side by side such that: theradiation generating quantum well structure and the radiation emittingregion of the pump radiation source lie at a same height above thecommon substrate; and a pump radiation from the pump radiation source isbeing laterally coupled into the radiation generating quantum wellstructure during operation of the optically pumped surface emittingsemiconductor laser device.
 3. An optically pumped surface emittingsemiconductor laser device according to claim 2, wherein: the radiationgenerating quantum well structure is being surrounded by the edgeemitting semiconductor structure; and the pump radiation source is again guided radiation emitting active region defined by a currentinjection path on a surface of the edge emitting semiconductor laserstructure.
 4. An optically pumped surface emitting semiconductor laserdevice according to claim 2, wherein: the radiation generating quantumwell structure is being surrounded by the edge emitting semiconductorstructure; and the pump radiation source is an index guided radiationemitting active region that is defined a current injection path on asurface of the edge emitting semiconductor structure in combination withtrenches in the edge emitting semiconductor structure formed along acurrent injection path.
 5. An optically pumped surface emittingsemiconductor laser device according to claim 4, wherein ends of currentinjection paths facing toward the radiation generating quantum wellstructure include a spacing of 10 μm-50 μm therefrom.
 6. An opticallypumped surface emitting semiconductor laser device according to claim 2,wherein: the common substrate is being composed of a material beingtransmissive for a laser beam generated in the optically pumped surfaceemitting semiconductor laser device; and a resonator mirror layer withan optimally substantially high reflection coefficient is being appliedon a side of the radiation generating quantum well structure facing awayfrom the common substrate.
 7. An optically pumped surface emittingsemiconductor laser device according to claim 1, wherein the pumpradiation source includes two pump radiation sources being arranged atopposite sides of the radiation generating quantum well structure, saidtwo pump radiation sources for emitting pump radiation into theradiation generating quantum well structure during operation.
 8. Anoptically pumped surface emitting semiconductor laser device accordingto claim 7, wherein the two pump radiation sources together form a laserstructure for an optical pumping with laser emission.
 9. An opticallypumped surface emitting semiconductor laser device according to claim 1,wherein the pump radiation source includes a plurality of pump radiationsources being arranged in a star like manner around the radiationgenerating quantum well structure, said plurality of pump radiationsources for emitting pump radiation into the radiation generatingquantum well structure during operation.
 10. An optically pumped surfaceemitting semiconductor laser device according to claim 1, wherein thepump radiation source include a ring laser.
 11. An optically pumpedsurface emitting semiconductor laser device according to claim 10,wherein the radiation generating quantum well structure is arrangedwithin a resonator of the ring laser.
 12. An optically pumped surfaceemitting semiconductor laser device according to claim 11, wherein theresonator of the ring laser is formed by an annularly closed waveguide.13. An optically pumped surface emitting semiconductor laser deviceaccording to claim 10, wherein the edge emitting semiconductor structureis being surrounded by a medium with a refractive index being less thana refractive index of the edge emitting semiconductor structure.
 14. Anoptically pumped surface emitting Semiconductor laser device accordingto claim 10, wherein the edge emitting semiconductor structure issurrounded by at least one of a gaseous medium and a dielectric.
 15. Anoptically pumped surface emitting semiconductor laser device accordingto claim 10, wherein the edge emitting semiconductor structure is beingformed as a cylindrical body with one of a circular and annular crosssection.
 16. An optically pumped surface emitting Semiconductor laserdevice according to claim 10, wherein the edge emitting semiconductorstructure is being formed as a prismatic body with a cross section in aform of one of a polygon and a polygonal ring.
 17. An optically pumpedsurface-emitting semiconductor laser device according to claim 1,wherein the edge-emitting semiconductor structure includes an activelayer embedded between said first waveguide layer and said secondwaveguide layer, said first wave guide layer and said second waveguidelayer being embedded between a first cladding layer and a secondcladding layer.
 18. An optically pumped surface emitting semiconductorlaser device according to claim 17, wherein: a boundary surface betweenthe edge emitting semiconductor structure and the radiation generatingquantum well structure is partially reflective.
 19. An optically pumpedsurface emitting semiconductor laser device according to claim 1,wherein: the edge emitting semiconductor structure includes a pluralityof active layers that are being connected in series with tunneltransitions, and the radiation generating quantum well structureincludes a plurality of quantum well groups that respectively lie at asame height above the common substrate as an active layer of the edgeemitting semiconductor structure.
 20. An optically pumped surfaceemitting semiconductor laser device according to claim 1, wherein: theradiation emitting quantum well structure and the pump radiation sourceare arranged above one another on the common substrate; and theradiation emitting quantum well structure is being optically coupled tothe edge emitting semiconductor structure, so that a pump radiation isbeing guided into the radiation emitting quantum well structure duringoperation of the optically pumped surface emitting semiconductor laserdevice.
 21. An optically pumped surface-emitting semiconductor laserdevice according to claim 20, wherein: the edge-emitting semiconductorstructure includes said first waveguide layer and said second waveguidelayer and an active layer, said active layer arranged between the firstwaveguide layer and the second waveguide layer; and the quantum wellstructure being epitaxially grown on the second waveguide layer, coversonly a sub-region of the edge-emitting semiconductor structure and isbeing optically coupled thereto, so that a part of the pump radiationgenerated in the edge-emitting semiconductor structure is being guidedinto the quantum well structure.
 22. An optically pumped surfaceemitting semiconductor laser device according to claim 21, wherein: thepump radiation source is a gain guided radiation emitting active regionbeing formed in the edge emitting semiconductor structure via acorrespondingly structured current injection path on a surface of thesecond waveguide layer.
 23. An optically pumped surface emittingSemiconductor laser device according to claim 22, wherein: the pumpradiation source is being formed in combination with correspondinglyetched trenches in the second waveguide layer.
 24. An optically pumpedsurface emitting Semiconductor laser device according to claim 21,wherein a refractive index of the second waveguide layer is higher thana refractive index of the first waveguide layer.
 25. An optically pumpedsurface emitting semiconductor laser device according to claim 21,wherein the active layer is being asymmetrically placed in the waveguideformed by the first waveguide layer and the second waveguide layer.